add-code-inspector-rule

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Add a new custom CodeInspector rule to detect problematic Wolfram Language patterns.
Changelog: Source: GitHub https://github.com/rhennigan/MCPServer
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---
name: add-code-inspector-rule
description: |
  Add a new custom CodeInspector rule to detect problematic Wolfram Language patterns.
  Use when asked to: "add a code inspector rule", "create an inspection rule",
  "add a lint rule", "detect [pattern] in code inspector", "add CodeInspector rule",
  "new code analysis rule".
argument-hint: "description of the rule to add"
---

# Add a Custom CodeInspector Rule

Follow this workflow to implement a new code inspection rule. The rule system lives in `Kernel/Tools/CodeInspector/Rules.wl` with tests in `Tests/CodeInspectorTool.wlt`.

## Step 1: Understand the Rule

$ARGUMENTS

Clarify these details (ask the user if not clear):

- **What code pattern should be detected?** Get an example of the problematic code.
- **Why is it problematic?** This becomes the inspection message.
- **Severity:** Fatal (code will not run, parse etc.), Error (almost certainly a mistake), Warning (likely a mistake), Remark (suggestion), Formatting (style).
- **Confidence:** 0.95 for highly certain rules, 0.9 for confident, 0.7-0.9 for likely.

## Step 2: Choose the Rule Type

| Type | When to Use | Add To |
|------|-------------|--------|
| **Abstract** | Match simplified AST patterns (most common) | `$customAbstractRules` in Rules.wl |
| **Concrete** | Need whitespace/comments (e.g., comment content) | `$concreteRules` in Rules.wl |
| **Aggregate** | Analyze relationships between multiple AST nodes | `$aggregateRules` in Rules.wl |
| **Text-level** | Raw source text (line length, file size, etc.) | `textLevelInspections` function in Rules.wl |

## Step 3: Explore the AST Structure

Use the `WolframLanguageEvaluator` tool to parse example code and understand its AST:

```wl
Needs["CodeParser`"];
(* For abstract rules: *)
CodeParser`CodeParse["problematic code here"]
(* For concrete rules: *)
CodeParser`CodeConcreteParse["problematic code here"]
```

Study the output to determine which node types and patterns to match. Key node types:
- ``CodeParser`CallNode`` — function calls like `f[x]`
- ``CodeParser`LeafNode`` — atoms like `42`, `"hello"`, `Symbol`
- ``CodeParser`InfixNode`` — infix ops like `a + b`
- ``CodeParser`PrefixNode`` — prefix ops like `-x`

**Note:** If you want to use symbols defined in `Rules.wl` in the WolframLanguageEvaluator tool during your exploration, you'll need to use their fully qualified names:

```wl
PacletDirectoryLoad["path/to/MCPServer"];
Get["Wolfram`MCPServer`"];
Wolfram`MCPServer`Tools`CodeInspector`Private`astPattern[...]
```

## Step 4: Read the Current Rules File

Read `Kernel/Tools/CodeInspector/Rules.wl` to understand the current state and find the right insertion points.

## Step 5: Define Reusable Patterns (if needed)

If the rule needs reusable patterns, add them to the **Argument Patterns** section (near the top of Rules.wl, after the `Needs` statements):

```wl
$$myPattern = HoldPattern @ Alternatives[
    _SomeFunction,
    _AnotherFunction,
    SomeSymbol
];
```

## Step 6: Add the Rule Entry

### For abstract rules — add to `$customAbstractRules`:

```wl
$customAbstractRules := $customAbstractRules = <|
    (* ...existing rules... *)
    (* MyNewRule - short description *)
    myPattern -> inspectMyNewRule
|>;
```

**Pattern approaches (choose one):**

Direct AST pattern matching:
```wl
cp`CallNode[ cp`LeafNode[ Symbol, "FunctionName"|"System`FunctionName", _ ], { _ }, _ ] -> inspectMyRule
```

Using a test predicate:
```wl
cp`LeafNode[ Symbol, _String? myPredicateQ, _ ] -> inspectMyRule
```

Using `astPattern` for Wolfram-syntax-level patterns:
```wl
astPattern[ - $$yieldsDateObject ] -> inspectMyRule
astPattern @ HoldPattern @ ReadString[ __, CharacterEncoding -> _, ___ ] -> inspectMyRule
```

### For concrete rules — add to `$concreteRules`:

```wl
$concreteRules := $concreteRules = <|
    CodeInspector`ConcreteRules`$DefaultConcreteRules,
    (* ...existing rules... *)
    myConcretePattern -> inspectMyRule
|>;
```

### For text-level rules — add to `textLevelInspections`:

```wl
textLevelInspections[ code_String ] :=
    Module[ { lines },
        lines = StringSplit[ code, "\n", All ];
        Flatten @ {
            inspectLineLengths @ lines,
            inspectFileLength @ lines,
            inspectMyTextRule @ lines  (* Add here *)
        }
    ];
```

## Step 7: Write the Handler Function

Add the handler in the **Definitions** section of Rules.wl, using the appropriate subsection marker.

### Standard AST handler template:

```wl
(* ::***...:: *)
(* ::Subsection::Closed:: *)
(*inspectMyNewRule*)
inspectMyNewRule // beginDefinition;

inspectMyNewRule[ pos_, ast_ ] :=
    Enclose @ Module[ { node, as },
        node = ConfirmMatch[ Extract[ ast, pos ], _[ _, _, __ ], "Node" ];
        as = ConfirmBy[ node[[ 3 ]], AssociationQ, "Metadata" ];
        ci`InspectionObject[
            "MyRuleTag",
            "Description of the issue shown to the user",
            "Warning",
            <| as, ConfidenceLevel -> 0.9 |>
        ]
    ];

inspectMyNewRule // endDefinition;
```

### If the pattern matches against AST metadata, add a skip clause:

If you find that the pattern is producing duplicate matches, it might be matching against metadata. To verify this, try parsing the code and inspecting the metadata:

```wl
In[1]:= CodeParser`CodeParse["x = 1"]

Out[1]= CodeParser`ContainerNode[String, {CodeParser`CallNode[CodeParser`LeafNode[Symbol, "Set", <||>], {CodeParser`LeafNode[Symbol, "x", <|CodeParser`Source -> {{1, 1}, {1, 2}}|>], CodeParser`LeafNode[Integer, "1", <|CodeParser`Source -> {{1, 5}, {1, 6}}|>]}, <|CodeParser`Source -> {{1, 1}, {1, 6}}, "Definitions" -> {CodeParser`LeafNode[Symbol, "x", <|CodeParser`Source -> {{1, 1}, {1, 2}}|>]}|>]}, <|CodeParser`Source -> {{1, 1}, {1, 6}}|>]
```

Note that the ``CodeParser`LeafNode[Symbol, "x", <|...|>]`` appears twice: once in the `CallNode` tree and once in the `"Definitions"` metadata.

To avoid this, you can add a skip clause to the handler to skip the match:

```wl
inspectMyNewRule[ pos_, ast_ ] /; MemberQ[ pos, _Key ] := { };
```

This works because only metadata will have `Key[...]` positions:

```wl
In[2]:= Position[CodeParser`CodeParse["x = 1"], CodeParser`LeafNode[Symbol, "x", _]]

Out[2]= {{2, 1, 2, 1}, {2, 1, 3, Key["Definitions"], 1}}
```

### If extracting a string field (e.g., symbol name) for the message:

```wl
inspectMyNewRule[ pos_, ast_ ] :=
    Enclose @ Module[ { node, name, as },
        node = ConfirmMatch[ Extract[ ast, pos ], _[ _, _, __ ], "Node" ];
        name = ConfirmBy[ node[[ 2 ]], StringQ, "Name" ];
        as = ConfirmBy[ node[[ 3 ]], AssociationQ, "Metadata" ];
        ci`InspectionObject[
            "MyRuleTag",
            "The symbol ``" <> name <> "`` has an issue",
            "Warning",
            <| as, ConfidenceLevel -> 0.9 |>
        ]
    ];
```

### Text-level handler template:

```wl
inspectMyTextRule // beginDefinition;

inspectMyTextRule[ lines_List ] := MapIndexed[
    Function[ { line, idx },
        If[ someCondition @ line,
            ci`InspectionObject[
                "MyTextRuleTag",
                "Description of the issue",
                "Formatting",
                <| cp`Source -> { { First @ idx, 1 }, { First @ idx, StringLength @ line } }, ConfidenceLevel -> 0.95 |>
            ],
            Nothing
        ]
    ],
    lines
];

inspectMyTextRule // endDefinition;
```

### If the handler needs a test predicate, define it nearby:

```wl
myPredicateQ // beginDefinition;
myPredicateQ[ name_String ] := (* condition *);
myPredicateQ[ ___ ] := False;
myPredicateQ // endDefinition;
```

## Step 8: Write Tests

Add tests to `Tests/CodeInspectorTool.wlt` at the end, before the cleanup section (`Integration Tests - Cleanup`). Follow this exact pattern:

```wl
(* ::**************************************************************************************************************:: *)
(* ::Section::Closed:: *)
(*Custom Rules - MyRuleTag*)

(* ::**************************************************************************************************************:: *)
(* ::Subsection::Closed:: *)
(*inspectMyNewRule - Basic Detection*)
VerificationTest[
    $myRuleResult = CodeInspectorToolFunction @ <|
        "code" -> "problematic code here",
        (* only include additional parameters if needed for the test *)
    |>,
    _String,
    SameTest -> MatchQ,
    TestID   -> "MyRuleTag-Basic-ReturnsString"
]

VerificationTest[
    StringCount[ $myRuleResult, "Issue " ~~ DigitCharacter.. ~~ ": MyRuleTag" ],
    1,
    SameTest -> SameQ,
    TestID   -> "MyRuleTag-Basic-HasTag"
]

VerificationTest[
    StringContainsQ[ $myRuleResult, "Description of the issue" ],
    True,
    SameTest -> SameQ,
    TestID   -> "MyRuleTag-Basic-HasDescription"
]

VerificationTest[
    StringContainsQ[ $myRuleResult, "(Warning" ],
    True,
    SameTest -> SameQ,
    TestID   -> "MyRuleTag-Basic-HasSeverity"
]
```

**Always include:**
- A detection test (returns `_String` result containing the expected number of occurrences of the tag)
- A description test (message text appears)
- A severity test (correct severity in output)
- A false-positive test (clean code does NOT trigger the rule)

## Step 9: Verify

1. **Run the tests** using the `TestReport` MCP tool on `Tests/CodeInspectorTool.wlt`
2. **Run CodeInspector** on the modified `Kernel/Tools/CodeInspector/Rules.wl` to check for issues
3. Fix any failures and re-run until all tests pass

## Reference: Key Aliases in Rules.wl

These context aliases are used throughout the file:

| Alias | Context | Aliased Example | Target Symbol |
| --- | --- | --- | --- |
| `ci` | `CodeInspector` | ``ci`InspectionObject`` | ``CodeInspector`InspectionObject`` |
| `cp` | `CodeParser` | ``cp`CallNode`` | ``CodeParser`CallNode`` |

## Reference: Section Marker Format

Use this exact format for section/subsection markers in Rules.wl:
```
(* ::**************************************************************************************************************:: *)
(* ::Subsection::Closed:: *)
(*functionName*)
```
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